I have had a few suits drenched before, from trail-and-error, the best solution I have found is:
1. Put a hanger in the jacket and use a trouser-hanger for the trousers (do not use a hanger where the trousers need to folded) and leave outside to dry out. If you are not able to leave clothes outsiude without protection from rain, you could leaver them indoors.
2. Once dry, brush down both garments
3. Iron on a low heat
However, if someone does have a better...